The present invention relates to a spud system for a dredging vessel with a longitudinal direction, which spud system has wire suspension system coupled with a spud carrier for resiliently forcing said spud in a vertical stance.
In general a cutter suction dredgers is fitted with a spud carrier that allows the dredger to be pushed forward when the working spud mounted in the spud carrier has penetrated into the bottom.
For long times dredgers have been equipped with a wire suspension system to keep the spud carrier upright. This way torsion between spud carrier and dredging vessel is avoided and cutter production can be enhanced.
In circumstances where large external forces are exerted on the dredger due to sea currents, waves, swell or other causes, overloading of the spud and/or the spud carrier cylinder, which drives the spud carrier, must be prevented by allowing the spud carrier to give way to the load from a neutral position. The neutral position refers to the carrier and the spud wherein the spud takes a vertical stance.
However in view of production capacity of the cutter suction dredger, it is important that the neutral position of the spud carrier is a) well defined and that, b) after removal of the overload condition, the spud carrier quickly returns to that neutral position.
It is known for spud carriers that are held in vertical position by means of a wire system, the overload protection can be realized by allowing at least one of the sheaves to move. As a result the spud carrier will rotate and give way to the overload. Simply connecting a gas spring (accumulator) to this wire system prevents overloading to occur but has as a consequence that there is no well-defined fixed position of the spud before and after overload. Such a spud carrier system is known from WO2006130934 wherein an apparatus is disclosed for accommodating a substantially vertical spud of a dredging vessel with a longitudinal direction, comprising a spud carriage which is mounted for limited rotation around a horizontal transverse axis, wherein at least a first and a second spring means is arranged under bias between vessel and spud in the longitudinal direction for the purpose of absorbing a moment on the spud carriage, which first and second spring means compensate each other in the non-loaded situation of the spud; and—at least one spring means is provided with a spring force limiting means for limiting the tension in said spring element from a determined maximum moment on the spud carriage.